What do the adjectives “harmful” or “beneficial” mean when referring to a species of the animal kingdom? Should we give ourselves the right to eliminate certain insects such as the tiger mosquito which spreads serious pathologies throughout Europe (dengue fever, chikungunya, etc.)? Not easy to answer these questions, but this is the exercise to which the guests of the One Health evening will comply, this March 23 in Montpellier.
At the heart of the debate, Jérémy Bouyer, researcher from the Center for International Cooperation in Agronomic Research for Development (CIRAD), will explain how he implements the so-called “sterile insect” technique to eradicate the tiger mosquito or the fly. tsetse. And to address the ethical questions posed by these eliminations.
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The south of France is now home to the scary tiger mosquito. You are working to eradicate it using the sterile insect technique (SIT). What does it consist of?
Forgive me, I am going to dampen the hopes of your readers a little: the eradication of the tiger mosquito from France is still a somewhat distant outcome, because the TIS is not quite mature against this species. But the principle of this encouraging technique is to eliminate an insect by avoiding the massive use of insecticides, which are known to be harmful, especially to the environment. SIT consists of rearing millions of male mosquitoes in the laboratory, which we irradiate with X-rays. These rays damage their spermatozoa, without damaging the other cells too much, which makes these males healthy. When we release them in the target area, they are therefore able to be “competitive” with wild males and mate with females. These wild females will fertilize the eggs with their irradiated sperm, which will destroy the embryos. Within a few years, reduction or even eradication is a certain outcome.
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Isn’t releasing hundreds of millions of mosquitoes into the wild risky for humans?
No, because they are males, and only females bite and can transmit diseases.
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Where is the research?
We are currently experimenting with large-scale SIT on the tiger mosquito in China, Spain and Italy. In two or three years, we will know more about its results on transmitted diseases and once the World Health Organization recommends it, we will be able to use it in many other countries. I am quite confident: a program in which CIRAD is a partner recently eradicated the tsetse fly from the Niayes, a region surrounding Dakar and home to 80% of the population of Senegal. It is a very dense area in agriculture and livestock. The tsetse fly wreaked havoc there, mainly biting cattle. This sick cattle constituted so many proteins missing from the local diet. Thanks to the eradication of tsetse, Senegalese farmers can now safely import cattle breeds, which are more productive than indigenous breeds.
This is good news, but it raises an ethical question: are humans entitled to program the death of a species, even if it is harmful?
This question leads to several answers. If the species is not endemic to a territory, it is indeed perfectly possible to eradicate it. For example, the tiger mosquito, originally from China, arrived in mainland France in the early 2000s. It was not there before. Making it disappear will therefore not upset any French ecosystem balance. Now, if the species is endemic to a territory, as is the case of tsetse in the Niayes, this raises questions. Disposal should only be done after measuring the environmental cost-benefit.
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In this case, what weighed in favor of the elimination of tsetse?
First, the fact that the Niayes are, as I told you, a very densely populated area, where the ecosystems are already severely degraded. Then, the fact that tsetse populations remain quantitatively significant in other areas of Senegal, which are still wild and therefore sparsely populated and little cultivated. They are more generally in Africa. It is therefore not threatened with extinction.
You talk about an environmental cost-benefit calculation. Isn’t it a bit arrogant to think you know how to measure everything a species weighs in an ecosystem when we know so little about ecosystems?
Some species, such as the tsetse fly, have been studied for a long time, so we know its role quite well. But the reason why we know it so well is not insignificant: it causes damage to farms, economically quantifiable, and threatens human health. (by sleeping sickness, Editor’s note).
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It is to believe that the “usefulness” of a species for humans weighs heavily in the balance…
It’s true. This is called the “extrinsic value” of a species. Look how quick we are to protect bees because they pollinate for us and produce honey for us to eat. But these honeybees are sometimes harmful to the environment, hogging the pollen resources of other native bee species. Look again at the proliferating cat that we find so charming, as it destroys a considerable small fauna…
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But what service does a tsetse fly render to ecosystems and not to humans?
As it threatens livestock, tsetse dissuades farmers from letting their animals graze in certain protected areas: it plays a de facto beneficial role for local wild animals, which are not very sensitive to its bites. The female tsetse also has the particularity, unique in the insect kingdom, of keeping the egg in her uterus for ten days and of giving birth to larvae heavier than herself! This last feature, among others, contributes to its intrinsic value, which should not be overlooked. This does not prevent the need to eliminate it from certain spaces.
